Polyamides are excellent in dynamic properties or heat resistance, and hence, they are frequently used in the field of automotive components or field of electric and electronic components. In the field of electric and electronic components, a surface mounting process with high mounting efficiency of components is diffused, and heat-resistant polyamides with high heat resistance and excellent strength are diffused as a suitable material for forming those components. In addition, in recent years, from the viewpoint of environmental loading reduction, lead-free solders are adopted as a solder to be used in the surface mounting process. However, in view of the fact that the lead-free solders are relatively high in terms of a melting temperature, it is necessary to set up a temperature in a reflow step of the surface mounting process at a high level as about 260° C. For that reason, as the heat-resistant polyamide for forming components for the surface mounting process, among heat-resistant polyamides, those having a relatively high melting point are adopted.
Now, in the field of electric and electronic components, the components are likely required to have flame retardancy, and in many cases, it is necessary to achieve a V-0 grade in the UL94 standard of Underwriters Laboratories. Hitherto, materials having a bromine-based flame retardant compounded therein have been generally used as the heat-resistant polyamide for forming electric and electronic components. However, in view of heightened awareness of the environment in the recent years, some raw materials containing noxious lead or cadmium or the like are being restrained in their use. Also, with respect to halogen-containing compounds, such as bromine-based flame retardants, etc., there is a tendency that their use is evaded irrespective of evaluation results thereof, such as safety, substantial environmental loading, etc., and a demand for halogen-free flame-retardant polyamides is increasing.
Some halogen-free flame retardants to be compounded in polyamides are known. However, flame retardants to be compounded in a heat-resistant polyamide having a high melting point are required to have high heat resistance withstanding high temperatures at the time of melt kneading on the occasion of producing a polyamide resin composition, or at the time of molding processing on the occasion of producing a molded article, in addition to the high flame retardancy. This tendency is conspicuous especially in electric and electronic components going through a reflow step of the surface mounting process.
Phosphinic acid salts are known as a halogen-free flame retardant having high flame retardancy and heat resistance. For example, a flame-retardant polyamide molding material containing a specified polyamide having a diamine unit composed mainly of an alicyclic diamine unit and a phosphinic acid salt is known (see PTL 1). In addition, a molding material containing an aliphatic polyamide and a specified phosphinic acid salt is known (see PTL 2). Furthermore, a resin composition containing a specified semi-aromatic polyamide, a polyphenylene ether, and a phosphinic acid salt is known (see PTLs 3 and 4).
Certainly, molded articles including a polyamide resin composition as described above have high flame retardancy and heat resistance; however, there may be the case where on the occasion of going through a reflow step, the brightness is conspicuously lowered, or yellowing is generated.
This tendency is conspicuous especially in molded articles going through a reflow step in the presence of oxygen. The matter that the brightness is low before and after the reflow step, or that yellowing is generated after going through the reflow step, was a problem to be solved in obtaining a product having a desired color tone as a molded article after going through the reflow step of the surface mounting process for example, various connectors, such as blue connectors responding to the standard of USB 3.0, white connectors to be used for LED peripheral members, etc., or the like).